Paste composition for brazing and brazing method using the same

ABSTRACT

The invention provides a paste composition for brazing, which upon brazing, does not cause brazing insufficiency such as residual carbon in any type of industrial brazing furnace, can achieve an excellent outward appearance of a brazed portion after brazing and can be applied to any existing industrial brazing furnaces, as well as a brazing method using the same. The paste composition for brazing comprises a brazing powder, butyl rubber and an organic solvent, wherein the brazing powder comprises at least one member selected from the group consisting of copper brazing powder, brass brazing powder, silver brazing powder, phosphorus copper brazing powder, nickel brazing powder, gold brazing powder, palladium brazing powder, copper-manganese brazing powder, silver-manganese brazing powder and cobalt brazing powder. The paste composition for brazing is applied onto at least a part of a surface of one base material and then the one base material is brazed onto the other base material.

TECHNICAL FIELD

The present invention relates to a paste composition for brazing and abrazing method using the same, and in particular, to a paste compositionfor brazing containing a brazing powder upon joining a metal, ceramicsor graphite and a brazing method using the same.

BACKGROUND ART

A brazing method is one kind of joining method for metal, ceramics etc.,which falls into the category of welding method. In particular, thebrazing method is a method of brazing using a brazing material having amelting point of not less than 450° C. and lower than the melting pointof a base material to be brazed. Specifically, brazing is conducted inthe following manner. A brazing material applied onto the surface of onebase material is heated to a temperature at which the brazing materialis melted but the base material is not melted, whereby the meltedbrazing material is attracted by the capillary phenomenon toward ajoining surface of the other base material, to form a thin film of thebrazing material. Thereafter, the brazing material is solidified bycooling to join the one base material to the other material.

Metal used generally as a brazing material in brazing is used in theform of a plate, foil, wire, powder, or powder-containing paste.

The brazing material in the paste form among these forms is usedfrequently because it is suitable for application to a site onto whichthe brazing material in the form of a plate, foil, wire or powder ishard to apply, that is, a site where the brazing material easily dropsbefore or during brazing. The paste composition is composed essentiallyof a brazing powder, a binder and an organic solvent. As a bindersolution, brazing cement or the like is commercially available. When thebinder solution is used, it can be mixed with a commercial powderybrazing material to give a paste composition.

Brazing is carried out by using an industrial brazing furnace such as areducing gas atmosphere furnace, an inert gas atmosphere furnace or avacuum furnace. When a conventional paste composition is used inbrazing, a carbon component remains on a brazed portion after brazing,depending on the type of brazing furnace, which may generate residualcarbon etc. to cause brazing insufficiency. For example, a certain pastecomposition does not cause brazing insufficiency upon brazing in afurnace of a reducing gas atmosphere such as a hydrogen-containing gas,but causes significant brazing insufficiency such as residual carbonsometimes upon brazing in a furnace of an inert gas atmosphere such asargon gas, helium gas etc. or in a vacuum furnace. Accordingly, even ifa paste composition suitable for a base material as a subject to bebrazed is selected as a brazing material, the type of brazing furnaceused is sometimes limited in order to prevent brazing insufficiency andto achieve an excellent outward appearance of a brazed portion. This isextremely inconvenient in industrial production.

At present, a paste composition for brazing which can, regardless of thetype of industrial furnace, be applied to any type of brazing furnacehas never been obtained.

Accordingly, an object of the present invention is to provide a pastecomposition for brazing, which upon brazing, does not cause brazinginsufficiency such as residual carbon in any type of industrial brazingfurnace, can achieve an excellent outward appearance of a brazed portionafter brazing and can be applied to any existing industrial brazingfurnaces, as well as a brazing method using the same.

DISCLOSURE OF INVENTION

The present inventor made extensive study on factors causing brazinginsufficiency such as residual carbon etc., and as a result he foundthat brazing insufficiency is caused by a binder contained in the pastecomposition. Based on this inventor's finding, the present invention wasmade, and has the following characteristic constitution.

The paste composition for brazing according to one aspect of thisinvention comprises a brazing powder, butyl rubber and an organicsolvent, wherein the brazing powder includes at least one memberselected from the group consisting of copper brazing powder, brassbrazing powder, silver brazing powder, phosphorus copper brazing powder,nickel brazing powder, gold brazing powder, palladium brazing powder,copper-manganese brazing powder, silver-manganese brazing powder andcobalt brazing powder.

As used herein, the butyl rubber refers to an isobutylenemonomer/isoprene monomer copolymer.

The paste composition for brazing of the present invention comprisesbutyl rubber as a binder. The linkage between the isobutylene monomerand isoprene monomer in the butyl rubber is a linear chain and thus itsstructure is easily decomposed by heating. It follows that without beinginfluenced by an atmosphere in a brazing furnace, the butyl rubber iseasily decomposed by heating in a brazing process. When the presentpaste composition containing butyl rubber as the binder is used inbrazing, the binder is easily decomposed by heating in the brazingprocess, and can thus attain an excellent outward appearance of a brazedportion after brazing, without causing brazing insufficiency such asresidual carbon.

Preferably, the paste composition for brazing of the present inventioncomprises the brazing powder in an amount of at least 50 mass % and notmore than 95 mass % and the butyl rubber in an amount of at least 0.5mass % and not more than 10 mass %, respectively, based on 100 mass % ofthe paste composition. Preferably, the average particle diameter of thebrazing powder is at least 1 μm and not more than 175 μm.

The brazing method according to another aspect of the present inventioncomprises the steps of applying a paste composition for brazing havingthe above features onto at least a part of a surface of one basematerial and then brazing the one base material onto the other basematerial.

Preferably, the brazing method of the present invention is carried outin a vacuum furnace or in a gas atmosphere furnace. When brazing iscarried out in a gas atmosphere furnace, an argon gas and/or a heliumgas or a hydrogen-containing gas and/or an ammonia-containing gas isused more preferably as the atmospheric gas.

As described above, the butyl rubber contained in the paste compositionof the present invention is decomposed at an increasing temperatureduring brazing without being influenced by an atmosphere in a brazingfurnace. Accordingly, when the present paste composition comprisingbutyl rubber as the binder is used in brazing, the binder is heatedduring the brazing process to be easily decomposed so that afterbrazing, an excellent outward appearance of a brazed portion can beattained without generating brazing insufficiency such as darkening.

The viscosity of the paste composition of the present invention can beregulated suitably by incorporation of a solvent etc., and thus knowncoating methods can be used.

Further, the brazing method of the present invention can be practiced inany existing brazing furnaces.

The paste composition of the present invention is excellent in brazingproperties regardless of whether it is dried or not after application.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention are described.

The brazing powder contained in the paste composition of the presentinvention is a metallic brazing powder used generally at present, whichis copper brazing powder, brass brazing powder, silver brazing powder,phosphorus copper brazing powder, nickel brazing powder, gold brazingpowder, palladium brazing powder, copper-manganese brazing powder,silver-manganese brazing powder, cobalt brazing powder or the like. Asthe brazing powder, one kind of metallic brazing powder described aboveis used, but plural kinds of metallic brazing powder described above maybe mixed and used.

The amount of the brazing powder incorporated into the paste compositionis at least 50 mass % and not more than 95 mass %, preferably at least70 mass % and not more than 93 mass %, more preferably at least 80 mass% and not more than 90 mass %, based on 100 mass % of the pastecomposition. When the content of the brazing powder is less than 50 mass%, the viscosity of the resulting paste is low to deteriorate coatingproperties, while the metallic powder in the paste is easily separatedand settled during storage. On the other hand, when the content of thebrazing powder is higher than 95 mass %, the viscosity of the resultingpaste is high to deteriorate coating properties.

The average particle diameter of the brazing powder is at least 1 μm andnot more than 175 μm, preferably at least 3 μm and not more than 75 μm,more preferably at least 5 μm and not more than 45 μm. It is notpreferable that the average particle diameter of the brazing powder isless than 1 μm, because the content of oxygen in the brazing powder isincreased so that brazing insufficiency may be caused particularly whenthe atmosphere in the brazing process is not reductive. When the averageparticle diameter of the brazing powder is larger than 175 μm, theviscosity of the resulting paste is low to deteriorate coatingproperties, while the metallic powder in the paste is easily separatedand settled during storage.

The brazing powder is most preferably gas-spray spherical powder with alower content of oxygen, preferably gas-spray amorphous powder,preferably electrolyzed powder or scale-shaped powder. When a reducinggas such as hydrogen-containing gas, ammonia-containing gas or the likeis used as the atmospheric gas in the brazing process, the shape of thebrazing powder is not particularly limited. However, when an inert gassuch as argon gas, helium gas or the like is used as the atmospheric gasin the brazing process or when brazing is conducted under vacuum,brazing insufficiency may be caused even if the present pastecomposition containing butyl rubber is used as the binder when thecontent of oxygen in the brazing powder is high. In this case, gas-sprayspherical powder with a lower content of oxygen is used most preferablyas a brazing powder, and gas-spray amorphous powder is used preferably.

In the paste composition of the present invention, butyl rubber that isan isobutylene monomer/isoprene monomer copolymer is used as resinacting as a binder. The butyl rubber used is preferably the one having amolecular weight of 250,000 to 500,000. When the molecular weight ofbutyl rubber is less than 250,000, the viscosity of the resulting pastecomposition is low to deteriorate coating properties, while the metallicpowder in the paste is easily separated and settled during storage. Onthe other hand, when the molecular weight of butyl rubber is higher than550,000, the viscosity of the resulting paste composition is high todeteriorate coating properties.

The amount of the butyl rubber to be incorporated into the pastecomposition should be in the range of at least 0.5 mass % and not morethan 10 mass % based on 100 mass % of the paste composition, and ispreferably at least 1 mass % and not more than 6 mass %, more preferablyat least 2 mass % and not more than 4 mass %. When the content of thebutyl rubber is less than 0.5 mass %, the viscosity of the resultingpaste composition is low to deteriorate coating properties, thuslowering adhesion to a base material as a subject to be brazed. When thecontent of the butyl rubber is higher than 10 mass %, the effect of thebutyl rubber used as a binder is saturated, resulting in higher costs.

The organic solvent contained in the paste composition of the presentinvention is not particularly limited insofar as the butyl rubber can bedissolved therein, and for example, one member selected from toluene,hexane and octane or a mixture thereof can be used as the organicsolvent.

The amount of the organic solvent to be incorporated into the pastecomposition is an amount suitable for regulation of the viscosity of thepaste composition, and is regulated specifically in the range of atleast 3 mass % and not more than 45 mass %, preferably at least 5 mass %and not more than 20 mass %.

Known additives such as an anti-settling agent, a thixotropic agent etc.can be added to the paste composition of the present invention. By thisaddition, it is possible to improve shelf stability (prevention ofseparation of the brazing powder), coating properties (prevention ofdripping of the applied paste composition) etc.

The paste composition of the present invention can be used by applyingit onto a part or the whole of the surface of a base material as asubject to be brazed. Application of the paste composition onto a partof the surface of a base material means that a necessary amount of thepaste composition is applied onto a portion to be brazed. The amount ofthis paste composition to be applied can be determined by calculationfrom a necessary amount of the brazing material on a portion to bebrazed and the content of the brazing material in the paste composition.

The method of applying the paste composition of the present inventionmay be a known method, and a method of using a dispenser, screeningprinting, brushing, spraying or the like may be used.

After application, the paste composition of the present invention isdried at room temperature or at a temperature of about 30 to 150° C. ifnecessary. After application, the paste composition is completely driedbefore the brazing process. This is because when the paste compositionis not dried, the organic solvent in the applied paste composition israpidly gasified to generate a gas by which the applied pastecomposition may be scattered. However, when a furnace provided with apreheating chamber is used as the brazing furnace, the organic solventis removed in the preheating step, and thus it is not always necessaryto completely dry the paste composition after application, and the pastecomposition can be brazed even if it is dry to the touch or not dried.The “dry to the touch” means that the paste composition is dried to sucha degree that the composition, upon being pressed against a finger, doesnot adhere to the finger.

EXAMPLES

Each component was mixed in amounts (mass %) shown in Table 1 (Examples)and Table 2 (Comparative Examples) to prepare paste compositions.

In Tables 1 and 2, “Copper brazing powder” is copper brazing powder(JIS: BCu-1A) manufactured by Nippon Atomize Co., Ltd., which isamorphous powder of 99.6% or more purity passing through screen openingsof 75 μm in size. “Nickel brazing powder” is nickel (Ni) brazing powder(JIS: BNi-5) manufactured by Wall Colmony Co., which is spherical powderpassing through screen openings of 106 μm in size. “Silver brazingpowder” is silver brazing powder (JIS: BAg-7) manufactured by NipponAtomize Co., Ltd., which is amorphous powder of 99.6% or more puritypassing through screen openings of 175 μm in size. “Exon Butyl 268” is atrade name of butyl rubber manufactured by Exon Chemical. “Disparon 305”is a trade name of hydrogenated castor oil (thickener) manufactured byKusumoto Kasei Co., Ltd. “Ethyl Cellulose N-4” is a trade name of ethylcellulose resin manufactured by Dow Chemical. “BR-100” is acrylic resinmanufactured by Mitsubishi Rayon.

The prepared paste composition was applied linearly to a length of 30 mmby a dispenser (outlet inner diameter, 2 mm) onto one side of astainless steel plate (2×100×100 mm) i.e. a base material as a subjectto be brazed. After application, the paste composition was dried underthe drying conditions shown in Tables 1 and 2. In the “Paste dryingconditions” in Tables 1 and 2, “a” means that the paste is not dried,“b” means that the paste is dry to the touch, specifically by leaving itat room temperature for 1 hour, “c” means that the paste is completelydried, specifically by heating it at a temperature of 60° C. for 15minutes in air.

After the paste composition was dried, the stainless steel plate coatedwith the paste was transferred to, and brazed in, a brazing furnace ofthe type shown in Tables 1 and 2.

In “Type of brazing furnace” in Tables 1 and 2, “a” means a gasatmosphere furnace containing hydrogen (15%), “b” means a vacuum furnace(degree of vacuum <133×10⁻³ Pa (10⁻³ Torr)), and “c” means an argon gasatmosphere furnace (dew point <−60° C.).

The brazing temperature was 1120° C. where the copper brazing powder wasused as metallic powder for brazing, 1150° C. where the nickel brazingpowder was used, and 830° C. where the silver brazing powder was used.

After brazing was completed, the molten state of the brazing materialand the occurrence of residual carbon on the brazed portion of thestainless steel plate were observed with naked eyes. The observationresults are shown in Tables 1 and 2. In “Molten state of brazingmaterial” in Tables 1 and 2, “A” means that the brazing material isexcellent in flow, “B” means that the brazing material is slightly poorin flow, “C” means that the brazing material is poor in flow or is notmelted. In “residual carbon” in Tables 1 and 2, “A” means no residualcarbon, “B” means slight occurrence of residual carbon, and “C” means alarge darkened area to deteriorate its commodity value.

The results shown in Table 1 reveal that when the present pastecompositions containing butyl rubber as the binder were used, thebrazing material was excellent in molten state upon brazing in any typeof brazing furnace, and no residual carbon was generated.

On the other hand, the results shown in Table 2 reveal that when thecomparative paste compositions containing ethyl cellulose resin oracrylic resin as the binder were brazed in a reducing gas atmospherefurnace i.e. in a hydrogen-containing gas atmosphere furnace, thebrazing material was excellent in molten state and no residual carbonwas generated, while when they were brazed in a vacuum furnace, thebrazing material was excellent in molten state, but slight residualcarbon was generated, and when they were brazed in an inert gasatmosphere furnace, the brazing material was slightly poor in flow, anda large amount of residual carbon as a darkened portion was observed.TABLE 1 Paste composition 1 2 3 4 5 6 7 8 9 10 11 Copper brazing powder85 85 85 85 85 Nickel brazing powder 85 85 85 Silver brazing powder 8585 85 Exon Butyl 268 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6Disparon 305 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Toluene 12 1212 12 12 12 12 12 12 12 12 Paste drying conditions c c a b c c c c c c cType of brazing furnace a b c c c a b c a b c Molten state of brazingmaterial A A A A A A A A A A A Residual carbon A A A A A A A A A A A

TABLE 2 Paste composition 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18Copper brazing 85 85 85 85 85 85 powder Nickel brazing 85 85 85 85 85 85powder Silver brazing 85 85 85 85 85 85 powder Ethyl Cellulose N-4 2.62.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 BR-100 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.62.6 Disparon 305 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.40.4 0.4 0.4 0.4 Toluene 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 1212 12 Paste drying c c c c c c c c c c c c c c c c c c conditions Typeof brazing a b c a b c a b c a b c a b c a b c furnace Molten state of AA B A A B A A B A A B A A B A A B brazing material Residual carbon A B CA B C A B C A B C A B C A B C

The ethyl cellulose resin or acrylic resin has a complicated molecularstructure, and its linkage is hard to be cleaved even by heating, andthe cleaved site is considered to be irregular, and oxygen atoms arecontained in its molecular structure. Accordingly, it is considered thatin the Comparative Examples, the ethyl cellulose resin or acrylic resincontained as a binder in the paste leaves a carbon component in thebrazed portion after brazing, to generate residual carbon.

In the Examples described above, application of the paste compositionfor brazing of the present invention to a stainless steel plate as asubject to be brazed, but the paste composition of the present inventioncan be applied not only to stainless steel, but also to variousmaterials such as metallic materials, ceramic materials and graphite.The paste composition containing butyl rubber as the binder has beendescribed in the Examples, but it should be construed that any pastecompositions containing a material such as resin bringing about the samefunction as that of butyl rubber or having equivalent functions to thoseof butyl rubber also fall under the scope of the present invention.

It is construed that the embodiments and Examples disclosed above areshown for mere illustrative purposes and are not restrictive. It isconstrued that the scope of the present invention is determined not bythe above embodiments or the Examples but by the claims, and encompassesevery correction and modification in meaning equivalent to that of theclaims and within the scope of the present invention.

Industrial Applicability

The paste composition for brazing of the present invention and themethod of using the same are suitable for joining metal, ceramics orgraphite.

1. A paste composition for brazing comprising a brazing powder, butylrubber and an organic solvent, wherein the brazing powder includes atleast one member selected from the group consisting of copper brazingpowder, brass brazing powder, silver brazing powder, phosphorus copperbrazing powder, nickel brazing powder, gold brazing powder, palladiumbrazing powder, copper-manganese brazing powder, silver-manganesebrazing powder and cobalt brazing powder.
 2. The paste composition forbrazing according to claim 1, comprising the brazing powder in an amountof at least 50 mass % and not more than 95 mass % and the butyl rubberin an amount of at least 0.5 mass % and not more than 10 mass %,respectively, based on 100 mass % of the paste composition.
 3. The pastecomposition for brazing according to claim 1, wherein the averageparticle diameter of the brazing powder is at least 1 μm and not morethan 175 μm.
 4. A brazing method comprising the steps of applying apaste composition for brazing onto at least a part of a surface of onebase material and then brazing the one base material onto the other basematerial, wherein the paste composition for brazing comprises a brazingpowder, butyl rubber and an organic solvent, and the brazing powderincludes at least one member selected from the group consisting ofcopper brazing powder, brass brazing powder, silver brazing powder,phosphorus copper brazing powder, nickel brazing powder, gold brazingpowder, palladium brazing powder, copper-manganese brazing powder,silver-manganese brazing powder and cobalt brazing powder.
 5. Thebrazing method according to claim 4, wherein the step of brazing iscarried out in a vacuum furnace.
 6. The brazing method according toclaim 4, wherein the step of brazing is carried out in a gas atmospherefurnace.
 7. The brazing method according to claim 6, wherein an argongas and/or a helium gas is used as the atmospheric gas.
 8. The brazingmethod according to claim 6, wherein a hydrogen-containing gas and/or anammonia-containing gas is used as the atmospheric gas.